To a vehicle having an engine and an automatic transmission with which an engine output torque can be controlled independently of operation of the accelerator pedal by a driver, the concept “driving force control” may be applied. According to this concept, positive and negative target driving torques, which are calculated based on for example the degree to which the accelerator pedal is operated by the driver and operating conditions of the vehicle, are accomplished by using the engine torque and the gear ratio of the automatic transmission. Such control methods as those called “driving force request type” and “driving force demand type” are also classified into the above-described concept.
With this driving force control, a target driving torque can be determined to easily change dynamic characteristics of the vehicle. Under acceleration/deceleration (transient response), however, not only an inertia torque relevant to a change of the gear ratio of the automatic transmission with respect to time but also an inertia torque relevant to a change of the wheel speed with respect to time causes the driving torque to deviate from the target value. Thus, the torque has to be corrected.
Further, in the case where how the gear ratio should be changed is determined based on a transmission map using the throttle opening position and the vehicle speed, the following problems arise. If the driving source of the vehicle is an engine, a generated torque is increased as the throttle is opened to an increased degree. Therefore, in the case where the driver operates the vehicle to increase the requested driving force, the driving force can be increased in principle by increasing the degree to which the throttle is opened. However, the resultant characteristics are as follows. When the throttle is opened to a certain degree, the driving force generated from the engine is saturated, which means that even if the throttle is opened to a greater degree, the driving force is changed to only a small degree (driving force is not increased) (means that the characteristics are not linear but non-linear). Therefore, in the state where a relatively great driving force is generated from the engine, if the driving force request is made to slightly increase the driving force, the throttle opening position is changed to a large degree. Thus, the throttle opening position is changed to a large degree so that the gear ratio is changed to cross the gear-change line on the transmission map. In this case, there is a deviation between the target driving torque and the generated torque and thus the vehicle behavior intended by the driver is not implemented.
Japanese Patent Laying-Open No. 2002-087117 discloses a driving force control apparatus using a control specification that realizes a steady-state desired value for the driving force as well as a transient-state desired value for the driving force by way of tune control of the engine torque and the gear ratio, and accordingly a driving force as requested by the driver can be achieved and the power performance and the drivability can remarkably be improved.
The driving force control apparatus disclosed in the aforementioned publication, with a powertrain including an engine and a transmission, includes accelerator manipulated variable detection means for detecting a manipulated variable of an accelerator, vehicle speed detection means for detecting a vehicle speed, desired driving force calculation means for calculating a static desired driving force based on the detected manipulated variable of the accelerator and the detected vehicle speed, driving-force pattern calculation means for calculating a desired driving-force change pattern, steady-state desired value calculation means for calculating a steady-state desired engine torque value based on the desired driving force and calculating a steady-state desired gear ratio based on the detected manipulated variable of the accelerator and the detected vehicle speed, transient-state desired value calculation means for calculating a transient-state desired engine torque value and a transient-state desired gear ratio, based on the desired driving-force change pattern, desired engine torque realization means for realizing the steady-state desired engine torque value as well as the transient-state desired engine torque value, and desired gear ratio realization means for realizing the steady-state desired gear ratio as well as the transient-state desired gear ratio.
With this driving force control apparatus, while the vehicle is running, the desired driving force calculation means calculates the static-state desired driving force based on the manipulated valuable of the accelerator detected by the accelerator manipulated variable detection means and the vehicle speed detected by the vehicle speed detection means, and the driving force pattern calculation means calculates the desired driving force change pattern. The steady-state desired value calculation means calculates the steady-state desired engine torque value based on the desired driving force and calculates the steady-state desired gear ratio based on the detected accelerator manipulated variable and the detected vehicle state, the transient-state desired value calculation means calculates the transient-state desired engine torque value and the transient-state desired gear ratio based on the desired driving force change pattern. Then, the desired engine torque realization means realizes the steady-state desired engine torque value and the transient-state desired engine torque value, and the desired gear ratio realization means realizes the steady-state desired gear ratio and the transient-state desired gear ratio. In other words, the inertia torque generated resulting from delay in gear shift of the transmission and change in rotational speed is not entirely compensated for by the engine torque. Instead, the control specification is provided to achieve the steady-state desired value for the driving force and the transient-state desired value for the driving force by way of tune-control of the engine torque and the gear ratio. Thus, the driving force as requested by the driver can be accomplished and the power performance and the drivability can remarkably be improved.
The driving force control apparatus disclosed in Japanese Patent Laying-Open No. 2002-087117, however, calculates the static-state desired driving force based on the accelerator manipulated variable determined by operation by the driver, and transient characteristics are calculated based on the desired driving force change pattern together with a delay occurring in each component of the vehicle, so as to determine the desired driving force. Therefore, regarding this calculation, operation by the driver and characteristics of each component of the vehicle (delay characteristics) are associated with each other. Thus, it is indispensable, for achieving perceived acceleration or perceived deceleration sensed as desired by the driver, to stably implement transient characteristics of the acceleration of the vehicle.
The driving force control apparatus disclosed in the aforementioned publication cannot solve the following problems:
1) difficulty of adaptation based on characteristics of the driver, since operation by the driver and characteristics of each component of the vehicle (delay characteristics) are associated with each other; and
2) difficulty in implementing a desired driving force requested by the driver, because of the considerable non-linearity of such dynamic characteristics change (transient characteristics change) as delay characteristics of each vehicle component.